PSI - Issue 26

Aleksa Milovanović et al. / Procedia Structural Integrity 26 (2020) 299 – 305 Milovanović et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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In both XFEM analysis highest stress states are located on and in the vicinity of the crack front. Created XFEM analysis considers ratio between minimal and maximal load as R=0, i.e. the numerical model after applied load is unloaded -similarly as in walking cycle. The XFEM analysis of total hip replacement implant numerical model with 14.6mm neck thickness can withstand 5.2 million walking cycles from the occurrence of the crack until structural failure while a numerical model with 9mm neck thickness can do 1.56 million cycles. Hence, the implant with the highest angular movement has 3.3 times lower structural life than original implant. Figure 7 shows the dependence of the number of walking cycles and crack length.

Figure 7. Diagrams showing dependence of crack length (ordinate) vs. number of walking cycles (abscise) (Up-14.6 mm diameter implant, Down-9 mm diameter implant)

Total hip replacement implant with 14.6 mm neck thickness has a maximal crack length of 15.28 mm, and implant with 9 mm neck thickness fails at only 3.45 mm crack length (Fig. 7). Caption of final step of fatigue crack propagation before structural failure for both numerical models are shown in Fig. 8, indicating that 9 mm neck thickness has a larger area under static failure. After about 5 million cycles implant with 14.6 mm neck thickness shows an occurrence of unstable crack propagation, while implant with 9 mm neck thickness has a stable crack growth throughout the entire crack propagation to failure. This behavior can be explained with much shorter crack length of the implant with the thinner neck and apparently larger area under static failure. Based on results presented here, one can conclude that the reverse Engineering allows efficient modelling of geometry of total hip replacement implant stem. Using CAD modelling software an existing digitized model may be redesigned according to demand. As a control for this endeavor FEM analysis was used in previous research [4] to locate areas with highest stress concentration, i.e. places with highest possibility of crack initiation. On selected total hip replacement implant highest stress states are located around the neck area. Previous research [4] shows that the thickness of the neck area affects the possible hip joint movement and structural life. In this paper, two total hip replacement implants are chosen from the group of five implants with a variation in neck thickness from original to 9 mm, in which 4. Conclusions